1. Field of the Invention
The present invention relates to a wireless communication terminal having a transmission power control function.
2. Description of the Related Art
There is a known technique for suppressing an increase in temperature of wireless communication terminals by decreasing a transmission output when a timer being operated during continuous transmission with normal power reaches a predetermined count value and furthermore by stopping the transmission output when a temperature sensor output exceeds a predetermined value (refer to, for example, Japanese Unexamined Patent Application Publication No. 2003-309473). There is another known technique for decreasing a transmission output when a preset allowable temperature is exceeded and increasing the transmission output to the original level when the temperature falls below the allowable temperature (refer to, for example, Japanese Unexamined Patent Application Publication No. 2002-271124). With still another known technique, when a temperature sensor output exceeds a preset reference value, transmission is restricted within a certain length of time so that the transmission is suspended after the certain length of time has elapsed and is completely disabled when the temperature further increases to exceed another reference value (refer to, for example, Japanese Unexamined Patent Application Publication No. H 04-326211). Furthermore, yet another known technique allows transmission to be suspended or a transmission output to be decreased for a certain period of time when transmission is continued for more than a restricted time frame set according to a transmission output mode (power) (refer to, for example, Japanese Unexamined Patent Application Publication No. H 09-214363).
Wireless communication terminals of PC card type used in card slots of personal computers (PC) generate a large amount of heat from a power amplifying section during transmission. Due to the structure of a wireless communication terminal of card type, heat generated in the manner described above is likely to remain in the card slot of the PC and is difficult to dissipate into the atmosphere outside, thus causing the service life of the wireless communication terminal itself and other devices to shorten. Possible approaches to this problem would be dissipating heat generated by the wireless communication terminal and to prevent the wireless communication terminal form generating extreme heat. Unfortunately, to dissipating generated heat is difficult because the wireless communication terminal of PC card type is mounted in a PC card slot during use. Therefore, the other approach of preventing the wireless communication terminal from generating extreme heat is a noteworthy, feasible solution to the problem.
However, the temperature control method described in, for example, Japanese Unexamined Patent Application Publication No. 2003-309473 is based on a simple control procedure, and is problematic in that there is danger of a guaranteed operating temperature upper limit being exceeded during transmission. Another problem with a wireless communication terminal used in a card slot is that the ambient temperature readily increases due to its structure, and this increased ambient temperature adversely affects the wireless communication terminal itself to cause the temperature thereof to increase.